The present invention relates to liquid polymer containing compositions for use as thickening agents in aqueous systems, and to the preparation of thickened aqueous well drilling and treating fluids.
Thickened aqueous mediums, particularly those containing oil field brines, are commonly used in well drilling, workover, and completing activities. Such aqueous media are also advantageously employed in hydraulic well treating and subterranean formation treating such as for the enhanced recovery of oil, as packer fluids, spacer fluids and hole abandonment fluids. In many cases, as for example in workover operations, the equipment at the well site is not as sophisticated as that commonly available at a drilling site. This is especially true in the case of equipment used for mixing fluids which are used in the workover operations. It is known to use hydrophilic polymeric materials such as hydroxyethyl cellulose (HEC) as thickening agents for aqueous mediums used in workover operations as well as in drilling, completion and other well treatment activities. However, it has been found that when HEC is added, in dry form, to an oil field brine to form, for example, a workover fluid, the fluid contains unhydrated lumps of polymer known as "fish eyes."
"Fish eyes" not only cause surface problems, such as screen blinding and reduced polymer yield, but also cause a variety of down hole problems. The unhydrated lumps of polymer can cause well damage by plugging perforations or plating out on the formation during open hole operations. Permeability impairment of gravel packs and blocking of screen and liner assemblies can also occur. The damage caused down hole by "fish eyes" is not easily reversed. The lumps of unhydrated HEC are inert in enzymes, chemical breakers and acids.